1. Field of the Invention
The present invention relates to a negative active material used in a manufacture of a lithium ion battery and a lithium ion battery including the negative active material, and more particularly, to a negative active material having high crystallinity and excellent high rate charge and discharge and good cycle characteristics during cyclic charge and discharge, and a lithium ion battery having the negative active material.
2. Description of the Related Art
A lithium ion battery generally includes a negative electrode and a positive electrode, and a separator disposed between the negative electrode and the positive electrode. The negative electrode provides electrons during a battery discharge, a positive electrode gains electrons provided by the negative electrode during the battery discharge, the separator sandwiched between said positive electrode electrically insulates the negative electrode and the positive electrode. A contemporary negative active material of the negative electrode used in the manufacture of a lithium ion battery includes various carbon materials, such as artificial graphite, natural graphite, hard carbon, and the like, and these carbon materials may intercalate and deintercalate lithium. In order to improve the performance of the lithium ion battery, many researches have been done on these carbon materials to obtain the improved utilization rate and charge density of electrode volume. The carbon materials have an actual charge capacity very close to the theoretical charge capacity (372 mAh/g) of graphite and thus have a disadvantageous limit in improving the charge density, therefore, the carbon materials are problematic in achieving high-capacity of a battery. The charge capacity here is a measurement for the charge capacity of the carbon materials per unit weight. Unit “mAh” refers to “amperes (mili amperes)×time (hours)”. Unit “g” refers to gram.
Accordingly, a metal lithium and a silicon alloy material have been researched as a negative active material, however, they have not been extensively used because of the stress accompanied by the expansion and the contraction of an electrode of the battery.
Additionally, a lithium vanadium oxide may be used as a negative active material with a higher capacity and a less stress induced by the expansion and the contraction of the electrode. Japanese Patent Laid-Open Publications No. 2002-216753, No. 2003-68305, and No. 2005-072008 disclose a lithium vanadium oxide.
Because the compound disclosed in Japanese Patent Laid-Open Publication No. 2002-216753 has no hexagonal crystal and has an equilibrium potential around 0.7V, such compound may not be appropriately used as a negative active material. In addition, the compounds disclosed in Japanese Patent Laid-Open Publication No. 2003-68305 and No. 2005-072008 not only have a disadvantageous significant change in the crystal structure accompanying intercalation and deintercalation of lithium ions during the charge and discharge of the battery, but also have problems during a procedure of the cyclic charge and discharge.